I see a lot of similarities between this bike and the number 5 bike that I am working on. It looks like it has the same wheels, sprockets, brake and front fork as number 5. The gas tank matches the number 5a picture. The bike I have has a fine thread gas cap like what my MK1s have. I suspect this cap is a quarter turn cap similar to the Stants on our MK3s and MK4s. The cap seems a bit flatter than the Stant so it might be an earlier version. I suspect my bike has a later MK2 gas tank because I do not see any green under the yellow paint.
I see 3 cables and a clutch actuating lever on the Albion side cover so I suspect this bike has a hand clutch in addition to a fluid drive like my bike has.
The slots in the drum wheel fill plug and the miter cap screw are both clocked the same as my number 5 bike. The front miter cap on my bike is clocked differently from the 5a picture but the drum wheel fill plug is clocked the same. The muffler looks very much like what is on my number 5 bike. Looks like my muffler has had the outlet moved from what would have been straight to the rear on the number 4 bike to straight to the rear on the my bike. I suspect this is the same muffler and they robbed parts from the number 4 bike to build my bike.
This bike has the Engray-Maico engine and the right side shifter. The shifter handle appears to be bent forward a bit maybe in an attempt to facilitate foot shifting. The clutch cover is big enough to go over an engine mounted fluid drive. It looks like the driver sprocket is outboard of the fluid drive instead of inboard like number 5.